Unidirectionally conducting elements



Aug. 27, 1957 J. M. N. HANLET 2,304,530

UNIDIRECTIONALLY CONDUCTING ELEMENTS Filed June 29, 1954 F l 6.4 INVENTOR.

' JACQUES MARIE uos'l. HANLET A T TORNEY United States Patent 2,804,580 UNlDlRECTIONALLY CONDUCTHNG ELEMENTS Jacques Marie Noel Hamlet, Paris, France, assignor to .l. Visseaux S. A., Paris, France Application June 29, 1954, Serial No. 440,155 Claims priority, application France August 13, 1953 28 Claims. (Cl. 317-=-234) The present invention relates to improvements in the constitution and manufacture of contact rectifier of diode elements including at least one layer of semi-conductive material such as germanium or the like, these elements being intended to be substituted to some kinds of vacuum or gas filled valves or tubes in electrical signalling, translating or calculating circuits.

One object of the invention is to provide such an improved constitution of these elements that it enhances their strength, both from the mechanical and from the electrical points of view.

Another object of the invention is to so provide such an improved constitution that such fragile components as cat-whiskers are eliminated therefrom.

Another object of the invention further is to so provide such an improved constitution that the resulting unidirectionally conducting therefrom may also be used in substitution to diode valves in such circuits as power supplies.

A further object of the invention is to so provide such an improved constitution that it may be obtained through a method of manufacturing which is simple and of high industrial efficiency in that the final products therefrom present substantially constant electrical characteristics of operation.

Another further object of the invention is to so provide such an improved constitution of these elements that they may incorporate means suitable for enabling a fairly high degree of natural or artificial cooling therefor if and when required in their practical use.

Still another object of the invention is to so provide such an improved constitution of these elements that they may be efficiently protected without any recourse to glass envelopesor the. like.

According to the invention, a unidirectionally conducting element comprising at least one layer of a semiconductive material such as germanium or the like is mainly characterised in that, to such a semi-conductive layer, is'superimposed a dielectric layer which is made discontinuous in that it presents, at least at the molecular scale, a network of tightly joined meshes, and to that dielectric layer is superimposed a continuous conducting film contacting said semi-conductive layer through substantially all the meshes of said dielectric layer.

According to the invention further, it is provided to obtain such a structure by depositing this dielectric layer over said semi-conductive layer and then by depositing said conductive film over said dielectric layer and, in some cases, by firstly depositing said semi-conductive layer over a base plate, prior to the above defined further deposits. The said dielectric layer may consist of a ceramic layer of high dielectric factor and consequently may be deposited over the said semi-conductive layer by evaporation under vacuo, or it may consist of a dielectric oxide such as alumina and consequently may be deposited by a cataphoretic process. As the said continuous conductive film may be formed by a process of evaporation in vacuo, as Well as, when required the deposition of the ice semi-conductive layer upon a base plate, all the steps of manufacturing of an unidirectionally conducting element according to the invention may be made within a single evacuated vessel, but for the subsequent fixation of the electrical contacts therefore which may be made for instance by mere soldering of lead-in Wires to said metallic film, and also, if and when requested, for the further enrobing of the complete assembly with a protective plastic material or waxy material.

These and further features of the invention will be described in detail with reference to the accompanying drawings wherein:

Figs. 1 and 2 show, respectively in a cross-section view and in a perspective view, a first illustrative embodiment of a unidirectionally conducting element according to the invention; and

Figs. 3 and-4 similarly show another illustrative embodiment of such an element.

In both Figs. 2 and 4, certain components are cut off in order to better disclose their assembly relationship.

Referring to Figs. 1 and 2, a germanium crystal is shown at 1, obviously with a fairly enlarged scale. The cubical shape of this crystal further is merely illustrative and a cylindrically shaped crystal, for instance, may as well be used.

A layer of a dielectric material such as alumina or silica is shown at 2, being deposited over the said crystal 1. From the structure and the method of deposit of said dielectric layer 2, this material has a very small thickness and presents a great number of irregularly shaped and distributed loopholes or meshes through the bottoms of which appears the semi-conductive material 1 (at the macroscopic scale).

Over the upper face of the dielectric layer and the free surface of the semi-conductive material, or partly at least over this latter material, a conductive film 3 is so deposited that numerous contact points exist between said film and said crystal surface 1.

By means of a deposit of solder, of Woods metal for instance, 4, a conductor 5 is affixed to said conductive film 3. Instead of soldering, any pressure contact arrangement could be made for such an electric connection. However the soldered contact appears to be of advantage in that it enables the enrobing of the whole element by means of any suitable plastic or waxy material, as usual for electrical components of other kinds. No glass envelope with sealed-in terminals is necessary, which, as obvious, is a marked advantage for such an element.

In the embodiment shown in Figs. 3 and 4, the semiconductive material 1 has been previously formed by a suitable deposition process upon a base plate 6. This base plate may advantageously extend on either side of the semi-conductive layer 1 so that it constitutes a cooling fin integral with the complete structure.

In either embodiment, the place of a further cooling fin, 7, has been illustrated, said fin being hollowed out in its midst and soldered by the periphery of said hole and part of its annular portion to the conductive film 3, or brazed upon said film.

The above mentioned plastic or waxy material will not, in such cases, be moulded upon at least the outer parts of such cooling fins.

The rectifier or diode etfect of the complete element is quite apparent and does not necessitate any comment therefor.

The method of manufacture of such an element will be explained in relation to the embodiment shown in Figs. 3 and 4 since, for manufacturing an element such as shown in Figs. 1 and 2, the first step of operation merely will be omitted, the remaining steps being unchanged.

A base plate of a material such as aluminium, iron, zinc, etc. or such as an alloy of such metals, is brought before a station suitable for effecting upon it a deposition under vacuum of a semi-conductive material through an evaporation process. Considering germanium, this station includes a carbon made crucible brought .at a higher temperature than 1500 C. so that the germanium from this crucible issublimated in vacuo. The base plate upon which a suitable mask has .been provided constitutes at-leastone cold spotupon which the semi-conductorcondensates. Obviously, of course, apluralityof elements can be simultaneously manufactured over a same base plate, which will be cut after the completion of said plurality of elements.

vAfter the deposition ofsaid semi-conductive material and a further cooling .of the thus-coated base plate, a cooling which preferably is accelerated by means of water circulating within the=snpport.of the said baseplate, this intermediate product is brought-to'the next station which includes a crucible .containing a dose of silica, for ;in stance, and consequently is brought to a temperature of at least 1700" C. The silicaevaporatesand deposes upon the cool surfaces constituted by the exposed faces of the semi-conductive layers. Whereas the first operative step was maintained until a substantial quantityo f germanium was evaporated and condensed upon the base plate for asuitable thicknessof said layer upon said .base plate, the second step isonly maintained for the deposition of a quasi monomolecular layer of dielectric material upon the said semi-conductive layer. Thus is obtained a ceramic network layer consisting of a large plurality of macroscopic meshes.

After cooling the thus obtained intermediary product, it is brought to a final station within the concerned vessel, and at this station is operated thedeposition of the above defined conductive film upon the said dielectric layer. A further and slow cooling will then be-ensured.

Of course, at the second and third stations, any masks and deflectors as required have beenso provided as to avoid a too high temperature of thematrix bearing ,the products and also for adjusting the areas covered by the deposited materials.

After the thus obtained elements have been brought out of the vacuum vessel, they are cut and provided with their own electrical connections at will. When required, cooling fins such as 7 are soldered'to them.

Instead of evaporating silica, or similarly efiicient ceramic material, a metallic oxide may be used in-substitution thereof, such as alumina or the like. In such a case, and in view of reducing the-time interval necessary for the desposition of this oxide, it is of advantage to have recourse to a cataphoretic deposition process. The thicknessof the deposit is adjusted, as usual, from the degree of saturation of the bath and the density of the current within said bath of aluminium oxide or the like, within which has been brought and immerged the base plate bearing the germanium layer or the support ,of ;the germanium crystals, as the case may be; of course, said base plate or said support acts as the collector electrode for the insulating particles.

In any case, the deposition of the-conducting film may be obtained from an evaporationin vacuo of a metal such as silver, aluminum, and so forth.

Any change may be brought to the above-detailed steps and arrangements that falls within the scope of the invention as defined by the appended claims thereto.

Having thus described my invention, I claim:

1. A unidirectionally conducting element comprising at least one layer of a semi-conductive material such as germanium or the like, and superimposed thereupon a dielectric layer which is made discontinuous in that it presents at least at the molecular scale a network of tightly joined meshes, and superimposed upon said dielectric layer a continuous conducting film which contacts said semi-conductive layer through substantiallyxall the meshes in .said dielectric layer.

12. A unidirectionally conducting element according to claim 1, wherein said dielectric layer consists of a quasi monomolecular coating of a dielectric material formed over part at least of the surface of the said semi-conductive layer.

3. A unidirectionally conducting element according to claim 1, wherein said conductive film is obtained by a deposition of a metal upon the said dielectric layer.

4. A unidirectionally conducting element according to claim 3, wherein said conductive film also extends to a part of said semiaconductive material uncoated with the said dielectric material.

5. A unidirectionally conducting elementaccording to claim 3, wherein said deposition ofa metal film is obtained from a process of evaporation in vacuo of a metal over the surface to be coated therewith.

6. A unidirectionally conducting element according to claim 1, wherein said layer of a semi-conductive material consists of a previously made crystal.

7. A unidirectionally conducting element according to claim 1, wherein said layer of a semi-conductive material consists of a deposit of said materialupon a base plate.

8. A unidirectionally conducting element according to claim 7, wherein said'deposit is obtained from a process of evaporation in vacuo of said semi-conductive'material onto said base plate.

9. A unidirectionally conducting element according to claim 7, wherein said base plate ismade of an .electrically conducting material and further constitutesa cooling fin for, said element.

10. A unidirectionally conducting element according to claim 1, wherein a connection wire is soldered to said conductive film by ,means of a low melting temperature solder.

11. A unidirectionally conducting element according to claim 1, wherein apressure contact means is associated to the said conductive film for the electrical connection of the said element.

12. A unidirectionally conducting element according .to claim 1, wherein -,a plastic enrobing is at least partly provided for said element.

13. ,A method ,of manufacture of a unidirectionally conducting element comprising the steps of coatingasemiconductive crystal with a ,quasi monomolecular layer of a dielectric material, and thencoating said dielectric layer and part ofsaid-semi-conductive crystalaround said'layer with a metallic film, said dielectric layer presenting at least at molecular scale a network of tightly joined meshes permittingpassage of said metallic film. j

14. A method of manufacturing a unidirectionally conducting element comprising the steps of depositing ajlayer of substantial thickness of a SBIIIIzCQIldUCtlVB material upon a metallic base plate, coating said semi-conductive layer with a quasi monomolecular layer of .a dielectric material and then coating said dielectric layer and ;part' of' said semi-conductive layersurrounding said .dielectric layer witha-metallic film, said{dielectric layer presenting at leastat molecular scale a network of tightly joined meshes permitting passage of said metallic film.

15. A method of manufacturing a unidirectionallyconducting element according to claim 14, wherein the said dielectric material consists .ofsilica, and wherein the said step of coating-the semi-conductive layer .with this-material includes the step of evaporating in vacuo the said silica. heated ina crucible over the;cool surface constituted by said semi-conductive layer.

.16. .A' method of manufacturing a unidirectionally conducting elementaccording to claim 14, wherein the said dielectricmaterial consists of alumina, and wherein the saidstep of coating the semifconductive layer with this material includes the step of depositing thealumina layer upon said {semi-conductive material within acataphoretic bath of whichthe base plate supporting said semi-conductive layer constitutes a collectingelectrode therefor.

17. A method of manufacturing a unidirectionally conducting.elementaccording to claim 14, wherein the step of coating the said dielectric layer with a metallic film includes the step of evaporating said metallic deposit from a crucible in vacuo.

18. A method of manufacturing a unidirectionally conducting element according to claim 14, wherein the step of forming a semi-conductive layer upon a base plate includes the step of evaporating said semi-conductive material from a crucible in vacuo with the presence of heat.

19. A unidirectionally conducting element according to claim 1, wherein said conductive film is obtained by a deposition of a metal upon said dielectric layer, said conductive film extending to a part of said semi-conductive material uncoated with said dielectric material; and wherein said deposition of a metal film is obtained from a process of evaporation in vacuum over the surface to be coated therewith.

20. A unidirectionally conducting element according to claim 1, wherein a waxy enrobing is at least partly provided for said element.

21. A method of manufacturing a unidirectionally conducting element comprising the steps of coating a semiconductive crystal with a quasi-monomoleucular dielectric layer of silica by evaporating in vacuum said silica heated in a crucible over the cooled surface constituted by said semi-conductive crystal, said dielectric layer presenting at least at the molecular scale a network of tightly joined meshes permitting passage of said metallic film and coating said dielectric layer and part of said semi-conductive crystal around said layer with a metallic film.

22. A method of manufacturing a unidirectionally conducting element comprising the steps of coating a semi-conductive crystal with a quasi-monomolecular dielectric layer of alumina depositing the alumina layer upon said semi-conductive material within a cataphoretic bath of which the base plate supporting said semi-com ductive layer constitutes a collecting electrode therefor, said dielectric layer presenting at least at the molecular scale, a network of tightly joined meshes permitting passage of said metallic film and then coating said dielectric, layer and part of said semi-conductive crystal around said layer-with a metallic film.

23. A method of manufacturing a unidirectionally conducting element comprising the steps of coating a semiconductive crystal with a quasi-monomolecular dielectric layer evaporating said metallic film from a crucible in vacuum; said dielectric layer presenting at least at the molecular scale a network of tightly joined meshes permitting passage of said metallic film; and coating said dielectric layer and part of said semi-conductive crystal around said layer with a metallic film.

24. A unidirectionally conducting element comprising at. least one layer of a semi-conductive material such as germanium or the like, and superimposed upon at least a portion of the surface of said semi-conductive layer a dielectric layer of alumina which is made discontinuous in that it presents at least at the molecular scale a network of tightly joined meshes, and superimposed upon said dielectric layer a continuous conducting film which contacts said semi-conductive layer through substantially all the meshes in said dielectric layer.

25. A unidirectionally conducting clement comprising at least one layer of a semi-conductive material such as germanium or the like, and superimposed upon at least a portion of the surface of the said semi-conductive layer a dielectric layer of alumina which is made discontinuous in that it presents at least at the molecular scale a network of tightly joined meshes; said alumina being ob tained by a deposition of alumina upon the semi-conductive material from a cataphoretic process; and superimposed upon said dielectric layer a continuous conducting film which contacts said semi-conductive layer through substantially all the meshes in said dielectric layer.

26. A unidirectionally conducting element comprising at least one layer of a semi-conductive material such as germanium or the like, and superimposed upon at least a portion of the surface of the said semi-conductive layer a dielectric layer of silica which is made discontinuous in that it presents at least at the molecular scale a network of tightly joined meshes, and superimposed upon said dielectric layer a continuous conducting film which contacts said semi-conductive layer through substantially all the meshes in said dielectric layer.

27. A unidirectionally conducting element comprising at least one layer of a semi-conductive material such as germanium or the like, and superimposed thereupon a dielectric layer which is made discontinuous in that it presents at least at the molecular scale a network of tightly joined meshes, said coating of silica being obtained by a deposition of silica upon the semi-conductive material from a process of evaporation in vacuum, and superimposed upon said dielectric layer a continuous conducting film which contacts said semi-conductive layer through substantially all the meshes in said dielectric layer.

28. A unidirectionally conducting element comprising at least one layer of a semi-conductive material such as germanium or the like, and superimposed thereupon a dielectric layer which is made discontinuous in that it presents at least at the molecular scale a network of tightly joined meshes, and superimposed upon said dielectric layer a continuous conducting film which contacts said semi-conductive layer through substantially all the meshes in said dielectric layer, and an annular cooling fin attached upon said conductive film.

References Cited in the file 'of this patent UNITED STATES PATENTS 2,046,686 Kannenberg July 7, 1936 2,345,122 Herrmann Mar. 28, 1944 2,386,218 Kotterman Oct. 9, 1945 2,428,043 Searle Sept. 30, 1947 2,479,446 Wilson Aug. 16, 1949 2,496,432 Blackburn Feb. 7, 1950 2,498,714 Searle Feb. 28, 1950 2,613,301 Dunbar et al. Oct. 7, 1952 2,657,345 Stuetzer Oct. 27, 1953 

1. A UNIDIRECTIONALLY CONDUCTING ELEMENT COMPRISING AT LEAST ONE LAYER OF A SEMI-CONDUCTIVE MATERIAL SUCH AS GERMANIUM OR THE LIKE, AND SUPERIMPOSED THEREUPON A DIELECTRIC LAYER WHICH IS MADE DISCONTINOUS IN THAT IT PRESENTS AT LEAST AT THE MOLECULAR SCALE A NETWORK OF TIGHTLY JOINED MESHES, AND SUPERIMPOSED UPON SAID DIELECTRIC LAYER A CONTINUOUS CONDUCTING FILM WHICH CONTACTS SAID SEMI-CONDUCTIVE LAYER THROUGH SUBSTANTIALLY ALL THE MESHES IN SAID DIELECTRIC LAYER. 